1. Energy Statistics;BMWi—German Federal Ministry of Economics and Technology,2007
2. Energiehandbuch—Gewinnung;Rebhan,2002
3. DESTATIS—Federal Statistic Office, Germany, 2007.
4. Energy Agency NRW (official website), 2007, Energy in Companies, http://www.ea-nrw.de/unternehmen/.
5. Energy Efficiency Through Optimized Coordination of Production and Technical Building Services;Hesselbach,2008